Ultra-Cheap chip-amp suggestions please

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thermionic

thermionic

Well-known member
Joined
Jun 3, 2004
Messages
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Ok, I apologise in advance for soiling the forum with talk of consumer-grade audio, feel free to throw some cabbages if you wish :oops:

I've made quite a few discrete amps over the years, but never a chip-amp so this is quite new to me. Ideally the amp will be able to supply upwards of 30w rms into a 4 Ohm load indefinitely. Reliability is a major concern, it doesn't have to possess a distortion spec like a Krell, but the ability to work day-in-day-out at upwards of 20w into 4 Ohm would be a necessity.

There are affordable-ish discrete options (could base something on the Hitachi apps data) but they are still more than I'd like to spend, as it will involve procuring mosfets. I have built LM481 chip-amps before, but that's as far as I've gone down this road.

Any suggestions? Can anyone suggest a chip-amp schematic that fits the bill?

Thanks in advance,

Justin
 
Try and control your excitement guys :green:

After some truffling I came across this little blighter: http://sound.westhost.com/project19.htm

Unless advised otherwise I will be proceeding with construction, powered via a raw unregulated supply.

If you haven't seen it before, this site has a plethora of amp projects: http://www.discovercircuits.com/A/a-audioamp.htm

J

edit: Just saw your reply Bill, that first remark doesn't apply to you :) Will check the link, Cheers!
 
what about one of those gain clone jobs using a LM3886 or 3875? I'm undertakin one now...

Very easy circuit - on the datasheet :thumb:

There's also a wealth of info in the chipamp forum at diyaudio...
 
How about this?

Gainc.gif


Amp and powersupply on a 5*10cm board. The schematic is on the first page of the LM3875 datasheet. Output power 40-50W. Want a couple of boards?

Best regards,

Mikkel C. Simonsen
 
Hey, these one-chip amps are great for use in signal tracing, or audio pass tests in your workbench.

Just don't claim the C37 lacquer finish and wooden volume knob will make it sound like a $1000 amp. :) See the Brewery (audiophool) posting.
 
Mikkel,

Could I get a pdf/gif/jpg of the bottom side trace, so I can etch a couple myself?

Have all the parts already, haven't laid it out yet. Yet another of the cardboard boxes up on the project shelf =)

Was planning this for a bench amp.

my mail:

jon at feefifofum.com

Regards

ju
 
Think I'll pass on the "BYOB" amp, but Thanks for the suggestion Owel :shock:

Thanks to all for the suggestions, MCS's amp looks the ticket for a slacker like me, check your PMs Mikkel.

:thumb:

Justin
 
[quote author="fum"]Could I get a pdf/gif/jpg of the bottom side trace, so I can etch a couple myself?[/quote]
I will make them later tonight.

Best regards,

Mikkel C. Simonsen
 
> Reliability is a major concern, it doesn't have to possess a distortion spec

Yes, use sound.westhost.com/project19.htm, gainclone, any of the things based on National's Overture line or similar products from other brands. At 30 watts you are well within the Overture range (20W-68W), and the published THD specs are fine for any customer who does not demand a Famous Designer Label.

Roll-your-own gets into serious blow-up-proof hassles. Chip-amp makers know about user-abuse and have learned to do the details right. Aside from having a staff for this, as a monolithic hunk they can do temperature control that can't be done so easily in discrete. (Though some Crown power amps had an analog computer that kept track of V and A, multiplied and integrated to get an estimate of power device actual temperature....) And unless you have kept your pencil sharp and slide-rule greased, a roll-yer-own is not likely to get the THD specs that the Overtures give.

If you hate PCB fabication and stuffing, Amplimo and others offer good modules, but not as cheap as a DIY gainclone.

> feel free to throw some cabbages

OK . . . . . . . . . . . .
cabbages.jpg
 
owel,

I did a single-sided LM3875 board for a little amp to power my Stax headphones:
3875.gif

No onboard PS though. The actual full board just has two of these patterns on it - I was just bashing out something to listen to those headphones with. Let me know if it suits.
 
[quote author="mnats"]owel,

I did a single-sided LM3875 board for a little amp to power my Stax headphones:
3875.gif

No onboard PS though.[/quote]
Remember to put electrolytics on the power rails close to the chip. 10µF is mentioned as the minimum value, but 470µF or higher is recommended. My board includes space for those. Some of the "gurus" will probably tell you that the 470µF caps are big enough, and that no powersupply caps will be needed... I would prefer to add two 4700µF caps though.

Best regards,

Mikkel C. Simonsen
 
[quote author="fum"]Could I get a pdf/gif/jpg of the bottom side trace, so I can etch a couple myself?[/quote]
Here you are: http://stiftsbogtrykkeriet.dk/~mcs/LM3875/

The schematic and PCB layout is there. If I were going to make the PCBs myself, I would probably drill the holes first and then simply draw the tracks on both sides with a PCB pen. The layout is too simple for photo PCB...

Best regards,

Mikkel C. Simonsen
 
Hi Justin,

Yep, I second the Nat Sem power amp IC's. The "Overture" do have good power and THD specs:

Nat Sem Power Amps

I've had good results with the TDA2030 and TDA2040 too- minimal external parts count. Used them in headphone distribution and a "lab amp" (my lab, not this Lab :wink: )

OTOH, if you want something more "interesting", then try the ILP power-amp modules. They're reasonably cheap, save a lot of work, and can be mounted very easily in a case. Check out this PDF review from audioexpress:

ILP Power Amp Modules Review PDF

:thumb:

Mark
 
My mistake, I'm confusing two chips. I never finished or built the LM3875 board design; 56 watts is a bit of overkill for my Stax headphones!

What I made was a LM1875 board:
lm1875.gif

Sorry for the error!

I think those 'gainclone' people have claimed that smaller bypass caps "sound better". My goal was only to make a cheap and dirty amp to run my electret headphones with so I just went with the application notes. FWIW, I've never had a problem with low frequency oscillation with the suggested 100uF caps and the stereo LM1875 amp is as quiet as a mouse.

(edit)The goal was cheap and dirty but I only succeeded in the former! It's also clean as a whistle!
 

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